Recently, rechargeable electric storage devices such as battery cells, e.g., lithium ion cells and nickel hydrogen cells, and capacitors, e.g., electric double layer capacitors, are employed as a power source for vehicles, e.g., cars and motorcycles, and various appliances, e.g., mobile terminals and laptop computers.
Such an electric storage device includes a housing, an electrode assembly of a wound type housed in the housing, two current collectors electrically connected to the electrode assembly and housed in the housing, and an electrolyte solution housed in the housing. The positive electrode and the negative electrode, which serve as electrodes constituting the electrode assembly, each have a side edge portion, in which an active material layer is not formed, along the winding direction on a metal foil. The side edge portion of the positive electrode is located at one end in the direction of the winding axis (extending along the winding direction), and the side edge portion of the negative electrode is located at the other end in the direction of the winding axis. The side edge portions of the positive electrode and the negative electrode are connected to the respective current collectors.
In such electric storage devices, there is a demand for impregnating the electrode assembly with the electrolyte solution, while reducing the amount of the electrolyte solution to be housed in the housing, from the viewpoint of a reduction in weight, a reduction in cost, or the like. As a technique for impregnating the electrode assembly with the electrolyte solution, JP 2012-195085 A and JP 2012-182343 A, for example, can be mentioned.
JP 2012-195085 A discloses a battery cell in which the junction states of the positive electrode and the negative electrode in their junction regions with the respective current collectors are made different from each other so that the electrode density is reduced, or the total junction area is reduced, in one of the junction regions of the positive electrode and the negative electrode with the respective current collectors, as compared to the other of the junction regions thereof. JP 2012-182343 A discloses an electric storage device in which metal foils of the positive electrode and the negative electrode are wound into an ellipsoidal shape, and parts of their side edge portions in the form of overlapping arcs are joined together.